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Investment Securities - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2019
USD ($)
security
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Investments, Debt and Equity Securities [Abstract]      
Number of debt securities with unrealized losses (securities) | security 66    
Percentage of individual securities' amortized cost basis (percent) 0.90%    
Percentage of Company's total amortized cost basis of investment securities portfolio (percent) 0.40%    
Number of debt securities in continuous loss position for over 12 months (securities) | security 34    
Loss duration 12 months    
Aggregate unrealized loss $ 431,000 $ 3,120,000  
Gross gain on sale of investment securities 0 0 $ 0
Gross loss on sale of investment securities 0 0 $ 0
Accrued interest receivable for investment securities 894,000 1,076,000  
Securities pledged to secure public deposits $ 157,091,000 $ 157,198,000